Method and apparatus for electromagnetic confinement of molten metal

ABSTRACT

A method and apparatus for electromagnetic confinement of molten metal during strip casting of molten metal between two belts that wrap around entry pulleys to create a molding zone. The molten metal is delivered to a curved surface of each belt to form strip metal. The molten metal is contained within the molding zone by a pair of edge containment devices. The edge containment devices have a C-shaped magnetic member with an upper pole having an upper pole face and a lower pole having a lower pole face. Current flows through a coil wrapped around a core region of the magnetic member to create magnetic lines of force that flow between the upper pole face and the lower pole face. The C-shaped magnetic member is positioned such that magnetic lines of force pass through the edges of the two belts and the molten metal, and keep the molten metal within the molding zone. According to the present invention, the pole faces can have a positive angle, a negative angle, no angle relative to a horizontal, or a combination thereof. The pole faces have a curved shape to maintain a constant distance between the pole faces and the edges of the two belts. The magnetic member can be formed from a series of bonded elements, a series of elements mechanically held together, or from a solid core. In a particular embodiment, the magnetic member comprises two halves which are removably attached to the core to facilitate replacement of the coil wrapped around the core region.

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/038,671, filed Feb. 20, 1997.

BACKGROUND

[0002] The present invention relates to the continuous casting ofmetals, and more particularly, to the electromagnetic confinement ofmolten metal in a twin belt casting system.

[0003] The continuous casting of thin metal strip has been employed inthe prior art but with only limited success. Prior techniques for thecontinuous casting of metal strip have been limited to a relativelysmall number of alloys; it has been found that if the alloy content ofvarious metals such as aluminum alloy are increased, the as-cast surfacequality of the strip deteriorates.

[0004] One approach employed by the prior art in the strip cast ofmetals has been what has become known in the art as the twin drumcaster. Such devices include a source of molten metal supplied to thespace between a pair of counter-rotating, internally cooled drums. Themolten metal thus solidifies when it comes into contact with the drumsto form a cast metal strip; the drums also assert a compressive force onthe solidified metal, and effect hot reduction of the cast alloyimmediately after freezing. Such twin drum casters have enjoyed thegreatest extent of commercial utilization in the strip casting ofmetals. Nonetheless, they offer some serious disadvantages arising fromthe fact that the output of such casting systems is substantially lowerthan that for other strip casting techniques. In addition, twin drumcasting, while providing acceptable surface quality in the casting ofhigh purity aluminum (e.g., foil), suffers from the disadvantages ofpoor surface quality when used in the casting of aluminum having a highalloy content. In addition, twin drum casters also suffer from theproblem of centerline segregation of the alloy due to deformation duringsolidification.

[0005] Another conventional technique is the strip casting of metals,and particularly aluminum, involving a twin belt strip casting techniquein which two endless moving belts are positioned adjacent each to theother to define a moving molding zone between them. Cooling of the beltsis typically effected by contacting a cooling fluid with the side of thebelt opposite of the side in contact with the molten metal. Such twinbelt strip casting machines have the advantage over twin drum castingmachines of providing significant output of cast metal. However, becausecooling is typically effected by having a cooling fluid in contact withone side of the belt while either molten metal or a hot cast metal stripis in contact with the other side of the belt, such casting systems giverise to high thermal gradients over the thickness of the belt. Thosethermal gradients, dynamically unstable, cause distortion in the beltand, as a result, neither the upper nor the lower belt is substantiallyflat. The result is that the product thus produced has areas ofsegregation and porosity.

[0006] Substantial improvements in the strip cast of metals have beenachieved as described in U.S. Pat. Nos. 5,515,908 and 5,564,491, thedisclosures of which are incorporated herein by reference. Those patentsdescribe a substantially improved method and apparatus for use in thestrip casting of metals using a twin belt technique in which use is madeof two endless belts positioned adjacent each to the other to define amolding zone therebetween. At one end of the machine, the belts eachpass over an entry pulley which defines a curved surface as each beltpasses around the entry pulleys. The molten metal, as disclosed in U.S.Pat. No. 5,515,908, is supplied to the curved surface of both of thebelts in the molding zone at a time when the belts are supported by thepulleys over which they are advanced, thus, preventing any initialwarping of the belts as molten metal is supplied thereto. Thereafter,the cast metal strip is carried between the belts, and supported by thelower belt whereby both the molten metal and the hot cast strip transferheat to the belts. That heat is then removed from the belts at a timewhen the belts are not in contact with either the molten metal or thehot cast metal strip to substantially prevent, minimize or eliminate thehigh thermal gradients which have plagued the prior art. Furtherimprovements in the techniques described in U.S. Pat. No. 5,515,908 aredisclosed in U.S. Pat. No. 5,564,491 in which there is provided a systemto control the spacing between the entry pulleys whereby the entrypulleys exert a compression force on the substantially frozen cast stripat the nip of the entry pulleys, that compressive force being sufficientto cause elongation of the cast strip to ensure that the cast strip isin compression in the direction of travel after exiting from the nip tominimize cracking of the cast strip.

[0007] The strip casting techniques as described above and other stripcasting techniques require the use of a containment system to maintainmolten metal in the gap between the rolls of the caster. Up to thepresent, the casting system has employed mechanical edge dams to providecontainment of the molten metal. One of the principal advantages of thestrip casting system as described in the foregoing patents is that thesystem is capable of operation at tremendously high speeds. As a result,however, the mechanical edge dams heretofore employed have a short life.They tend to be worn out rapidly by erosion of the hot metal flowing athigh velocities in contact with such mechanical edge dams. In addition,such mechanical edge dams provide sites for the formation of skull whichhas a tendency to be sheared off and thus enters the cast to render themicrostructure metallurgically undesirable.

[0008] Electromagnetic edge dams have been employed in the prior art inthe strip casting of metals such as aluminum in twin drum castingsystems. Such systems have been generally categorized into one of twodistinct systems. The first are those systems that use a combination ofa magnet assembly and an AC coil to generate confinement forces andthose systems that rely solely on an AC coil to generate the containmentforces.

[0009] The magnetic systems use a magnetic member which comprises a yokeor core connecting two pole faces disposed on either side of the gap onwhich the molten metal is to be confined. The magnetic member is made ofa ferromagnetic material and surrounded over the given length of theyoke by a coil carrying an AC current. The magnetic flux generated bythe flow of the current in the coil is transmitted to the poles of themagnet through the yoke, and when the flux lines pass through the moltenmetal, they cause the flow of induced currents in the molten metal. Theinteraction between the applied field and these induced currentsestablishes containment forces at the metal surface in the gap.

[0010] Typically, in systems of that type, part of the magnetic memberis covered with an electrically conductive shield to minimize leakage offlux in a direction away from the gap. Such magnetic confinement systemshave the advantage that the confinement current need not be as high ascompared to those systems using solely an induction coil. If a strongermagnetic field is required, it can be achieved with the same currentlevel by reducing the area of the pole faces. Such systems are notwithout disadvantages, however. Such systems typically have pooroperating efficiency by reason of core losses and losses due to magnetichysterisis when an AC current is applied to the magnetic material. Inaddition, high amounts of heat are generated, necessitating the need forcooling systems to avoid damage to the magnetic system.

[0011] The induction coil type confinement system typically employs ashaped inductor positioned close to the gap in which the molten metal isto be contained. The AC current flowing in the inductor generatesinduced currents in the molten metal as well as a time-varying magneticfield on the surface of the molten metal. The current-magnetic fieldinteraction provides the containment forces. Such induction coil systemsare generally simpler in design than the magnetic systems. However, theinduction coil type systems are limited in terms of maximummetallostatic head which can be supported. That is because very highinductor currents are needed to provide the necessary containmentforces, and such high currents are accompanied by extremely high heatwhich in turn hinders or slows the solidification process.

[0012] One such magnetic confinement system is disclosed in U.S. Pat.No. 4,936,374, illustrating a magnetic type confinement system tosupport molten metal in the gap between the rolls of a vertical twinroll caster. Other electromagnetic confinement systems are disclosed inU.S. Pat. Nos. 4,974,661, 5,197,534, 4,986,339 and 5,487,421. Each ofthe systems disclosed in the foregoing patents is directed to anelectromagnetic containment system for use with twin drum castingapparatus as distinguished from twin belt casting apparatus. Thus, thecontainment forces need only be great enough to support themetallostatic head in the reservoir of molten aluminum maintained abovethe nip between the twin drums of the twin drum casting system. Incontrast, twin belt casters of the type described in U.S. Pat. Nos.5,515,908 and 5,564,491 present different types of containment problemsbecause of their unique configuration. For example, electromagnetic edgecontainment systems for use in U.S. Pat. Nos. 5,515,908 and 5,564,491must be capable of addressing the unique problem arising from thesqueeze pressure arising from belts positioned in a generally horizontalplane. Thus, there is a need to provide electromagnetic containmentsystems capable of use with twin belt casting systems of the typedescribed in the foregoing patents.

[0013] It is accordingly an object of the invention to provide analternative technique for edge containment which overcomes the foregoingdisadvantages.

[0014] It is a more specific object of the invention to provide atechnique for edge containment which is electromagnetic to producecontainment involving no physical contact between the molten metal andthe containment element.

[0015] It is yet another object of the invention to provide apparatusfor use in the strip casting of molten metal utilizing a pair of endlessbelts equipped with edge containment apparatus to efficiently provideedge containment of the molten metal.

SUMMARY

[0016] The concepts of the present invention reside in electromagneticedge containment apparatus for use in the strip casting of molten metalby means of a pair of endless belts. In the practice of the invention, apair of endless belts is positioned adjacent each to the other to definea molding zone therebetween. Each belt passes over an entry pulley anddefines a curved surface on the belt adapted to receive molten metal.The apparatus also includes means for supplying molten metal to thecurved surfaces of each of the belts, the molten metal being confined oneach of the lateral edges of the belts by electromagnetic apparatuspositioned on each side of the belts adjacent to the molding zone. Thus,the electromagnetic apparatus serves to electromagnetically confine themolten metal in the molding zone in contact with the curved surfaces.

[0017] In the practice of the invention, the electromagnetic apparatusincludes a magnetic member having an upper pole and a lower pole and aninduction coil wound about a core portion of the magnetic member wherebymagnetic lines of force pass from one of the upper and lower poles tothe other. The magnetic member is positioned adjacent each lateral edgeof the belt in the area of the molding zone so that the upper and lowerpole faces allow the magnetic lines of force to pass through the lateraledges of each of the belts to establish containment forces at the edgesof the belts to contain the molten metal in the molding zone between theedges of the belts.

[0018] It has been found that by positioning the magnetic memberadjacent to the edges of each of a ferromagnetic member such as thebelts in the molding zone, the magnetic lines of force from the poles ofthe magnetic member are attracted to the feromagnetic member in the formof upper and lower belts and thus serve to focus containment forces onthe molten metal maintained in the molding zone between the upper andlower belt. The attraction of the ferromagnetic member, that is themagnetic belts, thus serves to direct and conserve the energy and hencethe confinement forces, focusing those forces on the liquid metal in themolding zone at the edges of the belt.

[0019] In contrast, such electromagnetic edge containment apparatus asused in the prior art with twin drum casters typically involve loss ofsubstantial energy because the magnetic flux could become dissipated tothe drum. In this invention, the belts, formed of a magnetic metal,serve to focus the magnetic lines of force at the edge of the belts toensure adequate containment forces without substantial loss of energy.

[0020] According to the present invention, the pole faces can have (1) apositive angle relative to the horizontal so that the inter-pole-facegap is larger at the outside edge of each pole face than at the insideedge of each pole face, (2) no angle relative to the horizontal so thatthe inter-pole-face gap is the same at the outside edges of each poleface as at the inside edge of each pole face, (3) a negative anglerelative to the horizontal so that the inter-pole-face gap is smaller atthe outside edge of each pole face that at the inside edge of each poleface, or (4) a combination thereof. The configuration of the pole facesshould be chosen so as to create a strong magnetic field and a steepmagnetic field gradient across each pole face.

[0021] In some embodiments of the present invention, a mechanical edgedam precedes the electromagnetic edge dam so that both dams confine themolten metal in the molding zone. In other embodiments, theelectromagnetic edge dam is extended to completely replace themechanical edge dam.

[0022] According to the present invention, the ferromagnetic member canbe formed from layers that are bonded together, layers that aremechanically held together, or a solid core that is cut to form theinter-pole-face gap. In addition, the ferromagnetic member can be formedso that the upper and lower halves of the ferromagnetic member areremovably attached so as to facilitate the repair and maintenance of thecontainment system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a side view in elevation of a twin belt caster equippedwith an electromagnetic edge dam apparatus in accordance with thepractice of the invention.

[0024]FIG. 2 is a sectional view taken along the lines 2-2 in FIG. 1.

[0025]FIG. 3 is a sectional view of the electromagnetic edge damapparatus of the present invention illustrating the path of the magneticlines of force in relation to the belts of the caster and the moltenmetal therebetween.

[0026]FIG. 4 is a view in perspective of one magnetic member suitablefor use in the practice of the present invention.

[0027]FIG. 5 is a sectional view of an electromagnetic edge containmentapparatus in accordance with another embodiment of the invention.

[0028]FIG. 6 is a sectional view of another embodiment of the inventionillustrating the use of contoured belts.

[0029]FIG. 7 is a perspective view of an alternative embodimentillustrating a magnetic member having stepped pole faces.

[0030]FIG. 8 is a cross-sectional view like FIG. 3 illustrating anotherembodiment of the invention utilizing cooling channels within the corewinding.

[0031]FIGS. 9, 10, 11, and 12 illustrate different pole face angles andorientations in accordance with the present invention.

[0032]FIG. 13 illustrates an exemplary embodiment of the presentinvention wherein a mechanical edge dam is used in conjunction with anelectromagnetic edge dam.

[0033]FIG. 14 illustrates a solid structure from which a magnetic memberin accordance with the present invention can be formed.

[0034]FIG. 15 illustrates an exemplary embodiment of the presentinvention wherein a magnetic member has a split core design.

[0035]FIG. 16 illustrates an exemplary embodiment of the presentinvention wherein a magnetic member has two regions.

DETAILED DESCRIPTION

[0036] The apparatus embodied in the practice of the invention isillustrated overall in FIGS. 1 and 2 of the drawings illustrating astrip caster employing the concepts of U.S. Pat. Nos. 5,515,908 and5,564,491 equipped with electromagnetic edge containment apparatus inaccordance with the practice of this invention. As there shown, theapparatus includes a pair of endless belts 10 and 12 carried by upperpulley 14 and lower pulley 16. As will be appreciated by those skilledin the art, the belts 10 and 12 are likewise supported by additionalpulleys as disclosed in the foregoing patents which are not illustratedin the present drawings for purposes of simplicity. The pulleys are of asuitable heat resistant type, with one of the pulleys in each pair beingdriven by suitable motor means likewise not illustrated in the drawingsfor purposes of simplicity. Each of the belts 10 and 12 is an endlessbelt and is preferably formed of a magnetic metal which has lowreactivity or is nonreactive with the metal being cast. A number ofsuitable metal alloys, as is understood by those skilled in the art, maybe employed, including steel belts.

[0037] As illustrated in FIG. 1, pulleys 14 and 16 are positioned oneabove the other whereby the belts 10 and 12 passing over those pulleysdefine curved surface 18 and 20 as the belts 10 and 12 pass over thepulleys 14 and 16, respectively. Thus, the belts, and particularly thecurved surface 18 and 20, define a molding zone therebetween, with theminimum gap between them dimensioned to correspond to the desiredthickness of the metal strip being cast. As will be appreciated by thoseskilled in the art, the thickness of the metal strip being cast isdetermined by the dimensions of the nip between belts 10 and 12 passingover pulleys 14 and 16 along a line through the axis of pulleys 14 and16 perpendicular to belts 10 and 12.

[0038] While it is not illustrated in FIG. 1 for purposes of simplicity,it is some times desirable to include, as disclosed in U.S. Pat. No.5,564,491, the disclosure of which is incorporated herein by reference,an apparatus to rigidly fix the relative positions of pulleys 14 and 16.As described in the foregoing patent, means to fix the relativepositions of those pulleys may be a tension member, which is eitherfixed or adjustable, such as a turn buckle, a pillow block or ahydraulic cylinder as disclosed in U.S. Pat. No. 5,564,491. As describedin that patent, the means controlling the spacing between entry pulleys14 and 16 serves to effect a compressive force on the substantiallyfrozen cast strip at the nip between pulleys 14 and 16 to causeelongation thereof so that the cast strip is in compression in thedirection of travel after exiting from the nip to minimize cracking ofthe cast strip.

[0039] Molten metal to be cast is supplied to the molding zone throughsuitable metal supply means 22 such as a tundish, substantiallycorresponding in width to the width of the narrower of the belts 10 and12. As will be appreciated by those skilled in the art, the tundish is aconventional means of supplying molten metal to strip casters.

[0040] Thus, the molten metal flows into the molding zone definedbetween the curved surface 18 and 20 of belts 10 and 12, respectively,passing substantially horizontally from the tundish to fill the moldingzone between the curved surface 18 and 20. As is described in U.S. Pat.No. 5,515,908, the molten metal begins to solidify and is substantiallysolidified by the point at which the cast strip reaches the nip ofpulleys 14 and 16. As is described in U.S. Pat. No. 5,515,908, themolten metal flows substantially horizontally to provide a flowingstream of molten metal to the molding zone where it is in contact withthe curved surface 18 and 20 of belts 10 and 12, respectively, as thosebelts pass around pulleys 14 and 16. That serves to limit distortion ofthe belts and maintain better thermal contact between the molten metaland each of the belts as well as improving the quality of the top andbottom surfaces of the cast strip.

[0041] In accordance with the concepts of the invention, the castingapparatus is equipped with a pair of electromagnetic edge dams 24 and 26positioned immediately adjacent the molding zone defined by the curvedsurface 18 and 20 on each lateral edge of the belts 10 and 12 asillustrated in FIG. 2. Electrical current to the electromagnetic edgedam is supplied by means of electrical conduits 26 as illustrated inFIG. 1.

[0042] The details of the electromagnetic e

ited in detail in FIG. 3 of the drawing representing a sectio

aratus 24 illustrated in FIG. 2. In the preferred prac

romagnetic edge containment apparatus employed in t

a magnet type of confinement system as described above

aped magnetic member 30 as illustrated in FIG. 3. The magnetic member 30thus includes a core 32 having an upper arm or pole 34 and a lower armor pole 36 extending therefrom to define a generally C-shapedcross-section. As illustrated in FIG. 3, an induction coil winding 38,composed of a plurality of turns 40, is wound around the core 32 of themagnetic member 30.

[0043] As is also disclosed in FIG. 3, the upper arm 34 terminates in apole face 42 where as the lower arm 36 terminates in a pole face 44positioned adjacent belts 10 and 12, respectively, with the molten metal46 being maintained therebetween. The pole faces 42 and 44 thus definethe surface from which the magnetic lines of force generated by themagnetic element 30 with its induction coil 38 pass from one of the polefaces 42 to the other pole face 44 as illustrated by the magnetic linesof force 48 as show in FIG. 3. It is not important in the practice ofthe present invention whether the magnetic lines of force pass from theupper pole face 42 to the lower pole face 44 or vice versa.

[0044] In one practice of the invention, the magnetic member 30 isformed from a ferromagnetic material such as silicon steel, and can beformed from a solid piece of such ferromagnetic material. Alternatively,the magnetic member 30 can be formed from a series of laminated elementsmachined and secured together using mechanical means, an adhesive orlike means to yield the desired configuration. In many instances, theuse of such laminates is preferable since such laminates serve to moreuniformly distribute the flux lines in the magnetic member and reduceloss due to saturation of the magnetic member. In addition, for amagnetic member made of laminated ferromagnetic material, the electricalenergy dissipated as heat is also more evenly distributed and moreeasily removed, particularly where the adhesive employed to hold thelaminate elements together has good thermal conductivity.

[0045] Surrounding the magnetic member 30 is an outer shield 50, whichis preferably made of a material, and most preferably a metal, havingstructural rigidity and extremely high electrical and thermalconductivities. Particularly good results are obtained when the outershield 50 is fabricated of copper, although other metals such as silverand gold can likewise be used. The high electrical conductivity of theouter shield 50 aids in containing the magnetic lines of force withinthe magnetic member while the good thermal conductivity aids in thedissipation of heat from the overall apparatus. As will be appreciatedby those skilled in the art, the outer shield 50 may be provided withcooling channels therein or brazed tubes thereon to distribute coolingfluid through or at the surface of the outer shield to further aid inthe removal of heat generated by the electromagnetic field. For example,an inlet 52 can be employed to pass a cooling fluid through the outershield for removal from a discharge port 54 as illustrated in FIG. 3when additional cooling capability is required. Thus, the cooling fluidcan be passed through a conduit within the outer shield to remove heatgenerated by the electromagnetic field.

[0046] The electromagnetic edge dam employed in the practice of thepresent invention also includes an inner shield 56 dimensioned to fitwithin the C-shaped configuration of the magnetic member 30 asillustrated in FIG. 3. The inner shield 56 likewise serves to containthe magnetic lines of force generated by the coil 38 of the magneticmember 30, insuring that the magnetic lines of force are maintainedwithin the magnetic member 30. In addition, it is also possible, andsome times desirable, to include within the inner shield conduit meansfor the passage of a cooling fluid therethrough where it is desired toincrease the ability to dissipate heat from the magnet. It is alsopossible to do away with the inner shield; especially so when usinggrain oriented silicon steel laminates where the field lines prefer toflow within the laminates.

[0047] The relationship between the electromagnetic edge containmentapparatus and the belts is also illustrated in FIG. 3 of the drawings.As can be seen there, the upper belt 10 and the lower belt 12 define amolding zone with the molten or liquid metal 46 being positionedtherebetween. The lateral edges of the belts 10 and 12 are positionedadjacent to the inner shield so that the magnetic lines of force passingout of one of the upper pole face 42 and the lower pole face 44 passthrough the upper and lower belts 10 and 12 and the liquid metal 46. Themagnetic field lines thus establish the containment force preventing theliquid metal from spilling over the edges of the upper and lower belts10 and 12, respectively.

[0048] As indicated above, the belts employed in the practice of thepresent invention have ferromagnetic characteristics, causing them toattract flux lines to themselves and thereby minimizing field lossesbetween the poles 42 and 44. That in turn maximizes the field availableat the space between the belts. The magnetic nature of the belts alsominimizes the gradient of the magnetic field reducing the magneticpressure that can be generated. In accordance with the preferredpractice of the invention, it is important to embody a high gradientmagnetic field on the belt to produce sufficient magnetic pressure afterallowing for the reduction of the field gradient due to the magneticnature of the belts. To produce that desired high magnetic fieldgradient at the belts, it is preferred to orient the poles at an anglerelative to the belts. The lines of force illustrated in FIG. 3illustrate the effects of the belts in modifying the field linedistribution in the vicinity of the molding gap.

[0049] The exact placement of the lateral edges of the belts relative tothe electromagnetic dam is not critical to the practice of theinvention, and can be varied. It is generally sufficient that thelateral edges of belts 10 and 12 be positioned such that most, if notall, the magnetic lines of force pass substantially immediately throughbelts 10 and 12. That ensures that sufficient containment forces will begenerated to prevent the liquid metal from spilling over the lateraledges of the belt adjacent to the electromagnetic containment apparatus.

[0050] The configuration of one embodiment of the magnetic member 30 isshown in FIG. 4 of the drawing which includes the base portion or core32 about which the coil is wound, the coil winding having been omittedfrom FIG. 4 for purposes of simplicity. The magnetic element 30 alsoincludes upper and lower arms or poles 34 and 36, respectively, whichare formed integrally with the core 32, whether the magnetic element 30is a solid piece of metal or a laminated structure as described above.Formed in the leading edges of the arms or poles 34 and 36 are the polefaces 42 and 44.

[0051] The magnetic member 30 is preferably formed from a ferromagneticmaterial such as silicon steel. The magnetic member 30 can be formedfrom layers that are bonded together, layers that are mechanically heldtogether, or from a solid core. In some instances, the use of laminatesis preferred because there is a more uniform distribution of flux linesin the magnetic member and less loss due to saturation. If the laminatehas good thermal conductivity, the heat is more evenly distributed andeasier to remove. In other instances, it is better to mechanically holdthe layers together.

[0052] As shown in FIG. 4, the pole faces 42 and 44 have a curvaturecorresponding substantially to the curvature of the belts 10 and 12adjacent to the electromagnetic containment apparatus. It has been foundthat best results are generally obtained when the pole faces have anarcuate or curved configuration so as to maintain a constant distancebetween the belts 10 and 12 as they pass around their respective pulleysand the pole faces themselves.

[0053] As shown in FIG. 4, the pole faces of the magnetic member 30 havea substantially smooth surface corresponding to the curvature of thebelts passing around the respective entry pulleys. As will beappreciated by those skilled in the art, however, it is also possible,and sometimes desirable from the standpoint of economies in manufacture,to approximate a smooth curved surface with a surface formed of a seriesof stepped elements. A magnetic member utilizing such stepped pole facesis illustrated in FIG. 7 of the drawing.

[0054] As shown in that figure, the pole faces 42 and 44 are formed of aseries of discrete substantially rectangular faces 45 which approximatethe smooth curved pole faces as illustrated in FIG. 4. As will beappreciated by those skilled in the art, the use of such stepped polefaces represents a distinct advantage in economies in manufacture of themagnetic member 30. As shown in that figure, the core 32 may be equippedwith a cooling conduit 47 extending therethrough; in that way, a coolingfluid can be passed through the cooling conduit 47 to aid in thedissipation of heat generated by the electromagnetic field.

[0055] In the preferred embodiment as s

g of the lateral edges of the belts 10 and 12 relative to t

onveniently be controlled by utilizing pulleys 14 and 16

ce 58 which is axially of diminished width as compared

y 14. In that way, the belts 10 and 12 can be positioned in closerproximity to the electromagnetic containment apparatus by dimensioningthe belts to extend beyond the belt supporting surface 58 of the pulleys14 and 16 as illustrated in FIG. 3. In an alternative embodiment, it issometimes preferable as shown in FIG. 5 to provide an annular copperring 60 between the pulleys 14 and 16 and the electromagneticcontainment apparatus. That copper ring modifies the magnetic field inthe vicinity of the molding zone to prevent the magnetic lines of forcefrom entering the rolls 14 and 16.

[0056] In accordance with another variation of the present invention asshown in FIG. 6, it is sometimes desirable to configure the belts 10 and12 with lips 62 and 64, respectively Those lips can simply be formed byincreasing the thickness of the lateral edges 66 and 68 of belts 10 and12, respectively, so as to provide a lip area of increased beltthickness at the lateral edges of the belts. As shown in FIG. 6,providing belts with increased thickness toward lateral edges improvesthe magnetic field strength as well as the field distribution regionbetween the belts 10 and 12, thereby maximizing the containment forcesnear the molding zone.

[0057] In designing the electromagnetic containment apparatus employedin the practice of this invention, a number of different techniques canbe employed in dissipating heat generated by the electromagnetic field.In the embodiment illustrated in FIG. 3, the core windings 40 about thecore 32 can be, as illustrated in FIG. 3, made of solid metal such ascopper wire. Alternatively, as shown in FIG. 8, the windings 40 may beformed of an annular conductor having a central opening 41 extendingtherethrough. Thus, cooled water can be passed through the centralopening of the windings 40 to aid in the dissipation of heat generatedby the electromagnetic field.

[0058]FIGS. 9, 10, 11, and 12 illustrate different pole face angles andorientations in accordance with the present invention. FIG. 9illustrates a cross section of a magnetic member 30 wherein the polefaces 42 and 44 have a positive angle relative to the horizontal. Thepositive angle means that the inter-pole-face gap 43 increases as thedistance from the core increases, i.e. the inter-pole-face gap 43 isgreater at the outside edge of each pole face than at the inside edge ofeach pole face. The angle of the pole faces should be chosen so as tocreate a strong magnetic field and a steep magnetic field gradientacross the pole face. A pole face can have any desired angle such as 5,10, 15, 20, 25, or 30 degrees relative to the horizontal. It will beappreciated by those skilled in the art that as the inter-pole-face gap43 increases, the strength of the field across the gap decreases. As aresult, the containment forces created by the magnetic member shown inFIG. 9 are stronger at the inside edge of each pole face than at theoutside edge of each pole face.

[0059]FIG. 10 illustrates a cross section of a magnetic member 30wherein the pole faces 42 and 44 have no angle relative to thehorizontal. The zero angle means that the inter-pole-face gap 43 is thesame at the inside edge of each pole face and the outside edge of eachpole face. As a result, the magnetic field created by the magneticmember shown in FIG. 10 is relatively uniform across each pole face.

[0060]FIG. 11 illustrates a cross section of a magnetic member 30wherein the pole faces 42 and 44 have a negative angle relative to thehorizontal. The negative angle means that the inter-pole-face gap 43 isless at the outside edge of each pole than at the inside edge of eachpole face. As a result, the containment forces created by the magneticmember shown in FIG. 11 are stronger at the outside edge of each poleface than at the inside edge of each pole face.

[0061]FIG. 12 illustrates a cross section of a magnetic member 30 havinga reverse angle configuration. The pole faces 42 and 44 are parallel inpart and not parallel in part. The inside region of the pole faces 42and 44 have a negative angle relative to the horizontal. The magneticmember shown in FIG. 12 and the magnetic member shown in FIG. 11 bothresult in a narrower strip than the magnetic member shown in FIG. 9.When the magnetic member shown in FIG. 9 is used to contain moltenmetal, the magnetic forces are at a maximum at the very edge of thebelt. When the magnetic member shown in FIG. 11 or 12 are used tocontain molten metal, the magnetic forces are at a maximum farther intothe belt. As a result, the strip width would be lower when using magnetswith a design as shown in FIGS. 11 and 12 as compared to the designsshown in FIGS. 9 and 10.

[0062]FIG. 13 illustrates an exemplary embodiment of the presentinvention wherein a mechanical edge dam 55 is used in conjunction withan electromagnetic edge dam having a magnetic member 30. The magneticmember 30 is preceded by the mechanical edge dam 55. It is possible toreplace the mechanical edge dam 55 completely. However, as mentionedabove, the electromagnetic edge dam should curve to mirror the curvedsurface of the belts. When the pole faces 42 and 44 spread apart tomirror the curved surface of the belts, the inter-pole-face gap 43increases and the strength of the magnetic field across the gapdecreases. For this reason, the mechanical edge dam 55 is used inconjunction with the extended magnetic member 30 at the point where themagnetic field is the weakest. The mechanical edge dam 55 shown shouldideally have a ceramic-less surface and comprise magnetic material toreduce the reluctance at the mouth of the molding zone. A ceramicmaterial may also be used to make mechanical edge dam 55 if processconditions preclude the use of a metallic material.

[0063]FIG. 14 illustrates a solid structure 70 from which a magneticmember 30 in accordance with the present invention can be formed. Asmentioned above, the magnetic member 30 can be formed from layers thatare bonded together, layers that are bolted together, or a solid corethat is cut to form the inter-pole-face gap. It will be appreciated bythose skilled in the art that currents can be induced in the individuallaminates and that the currents can lead to the generation of heat. Forthis reason, it may be advantageous to cut the magnetic member from asolid core. If, for example, a silicon steel sheet is wound into aracetrack-like shape 70 that corresponds to the external shape of themagnet 30, the pole faces 42 and 44 can be formed from the block 70 byremoving a piece of metal 71 from the region where the inter-pole-facegap should be located, see the open region or gap in FIG. 15. Thismethod of manufacturing the magnetic member 30 is usually less expensivethan other methods of manufacturing. More importantly, when the siliconsteel is very thin (approximately 1 mil thick) this method minimizes theheat induced in a stacked design and facilitate the cooling of themagnetic member 30.

[0064]FIGS. 15 and 16 illustrate an exemplary embodiment of the presentinvention wherein a magnetic member 30 has a split core design. It willbe appreciated by those skilled in the art that as the containmentsystem is used, insulation around the induction coil 40 begins todeteriorate and has to be replaced. In conventional systems, the coil 40is replaced by dismounting the magnet 30 from the belt caster, cuttingthe coil 40, removing the coil 40, and winding a new coil (not shown)around the magnet 30. In addition, if the magnet 30 is

essary to replace the entire magnet 30.

[0065] According to the emb

mber 30 has a split core design wherein the

and/or a lower region 82 that is remov

the C-shaped magnetic member 30.

ce the induction coil 40. If the uppe

ed from the central region 80, it is possibl

a new pre-wound coil (not shown). Furt

egion 82 is damaged by one of the belts, i

et 30. The top and bottom regions 81 and 82 can be replaced byconnecting a new top or bottom region (not shown) to the central region80.

[0066] In the embodiment shown in FIG. 16, the magnetic member 30 has asplit core design wherein the magnetic member 30 is formed of laminatesand has an upper region 83 and/or a lower region 84 that attach to forma C-shaped magnetic member 30. It is easier to replace the inductioncoil in this design; the magnetic member is first disassembled, and anew pre-wound coil inserted before the magnetic member is reassembled.As stated above, if the upper region 83 or bottom region 84 is damagedby one of the belts, it will not be necessary to replace the entiremagnet 30. The damaged half of the magnetic member can be replaced byconnecting a new top 83 or bottom region 84. The upper 83 and lower 84regions are mechanically held together to maintain the properorientation. For example, bolts 85, 86 are used to hold the laminates ofeach half together. Thereafter, plates 87 on each end attach to the twobolts 85, 86 and keep the two regions together. It is preferred that thebolts and plates be made of non-magnetic material, preferably stainlesssteel.

[0067] It will be understood that various changes and modifications canbe made in the details of construction and use without departing fromthe spirit of the invention, especially as defined in the followingclaims.

What is claimed is:
 1. An apparatus for strip casting of molten metalusing electromagnetic edge containment comprising: (a) a pair of endlessmetal belts positioned adjacent each to the other to define a moldingzone therebetween, with each belt passing over an entry pulley to definea curved surface adapted to receive molten metal thereon, (b) means forsupplying molten metal to the curved surfaces of each of the belts tosupply molten metal thereto, and (c) edge containment apparatuspositioned on each side of the molding zone to contain the molten metalin the molding zone in contact with the curved surfaces, said apparatusincluding a magnetic member having an upper pole and a lower pole, aninduction coil wound about a portion of the magnetic member to generatemagnetic lines of force passing from one of the upper and lower poles tothe other, with the magnetic member being positioned such that the upperand lower poles direct magnetic lines of force through the edges of eachof the belts to establish containment forces at the edges of the beltsto contain the molten metal therebetween.
 2. An apparatus as defined inclaim 1 which includes shield means positioned about the magnetic memberto contain the magnetic lines of force within the magnetic member.
 3. Anapparatus as defined in claim 1 which includes an inner shieldpositioned within the magnetic member to contain the magnetic lines offorce to the magnetic member.
 4. An apparatus as defined in claim 1,wherein the magnetic member has a generally C-shaped configuration,including a core portion and parallel poles integral with and extendingtherefrom.
 5. An apparatus as defined in claim 4, wherein the poles ofthe magnetic member terminate in pole faces positioned adjacent theendless belts whereby the magnetic lines of force pass from one of thepole faces through the belts and to the other of the pole face tothereby establish containment forces for molten metal maintained in themolding zone between the endless belts.
 6. An apparatus as defined inclaim 4, wherein the induction coil is wound about the core of themagnetic member.
 7. An apparatus as defined in claim 1, wherein themagnetic member is formed of a ferromagnetic material from a series oflaminated elements secured together.
 8. An apparatus as defined in claim1 which includes shield means positioned between the magnetic member andthe entry pulleys to shield the entry pulleys from the magnetic lines offorce.
 9. An apparatus as defined in claim 5, wherein the pole faces arepositioned adjacent to and at an angle with respect to the endless beltsto ensure a gradient of magnetic flux at the lateral edges of theendless belts.
 10. An apparatus as defined in claim 1, wherein the beltseach have a lip formed by gradually increasing the thickness of thebelts at their lateral edges adjacent the edge containment apparatus,said lips serving to modify the strength and distribution of themagnetic lines of force to confine liquid metal between the belts. 11.An apparatus as defined in claim 1, wherein the magnetic member isformed of a ferromagnetic material from a stack of bonded elements. 12.An apparatus as defined in claim 1, wherein the magnetic member isformed of a ferromagnetic material from a plurality of sections that aremechanically held together.
 13. An apparatus as defined in claim 1,wherein the magnetic member is formed from a solid core of ferromagneticmaterial.
 14. An apparatus as defined in claim 1, wherein the pole facesare parallel.
 15. An apparatus as defined in claim 1, wherein the polefaces are not parallel.
 16. An apparatus as defined in claim 1, whereinthe pole faces have a first opposed surface parallel to each other and asecond opposed surface not parallel to each other.
 17. An apparatus asdefined in claim 1, wherein a distance between the pole faces is greaterat the outside edge of each pole face than at the inside edge of eachpole face.
 18. An apparatus as defined in claim 1, wherein a distancebetween the pole faces is greater at the inside edge of each pole facethan at the outside edge of each pole face.
 19. An apparatus as definedin claim 1, further comprising a mechanical edge dam that is positionedin a region along the belts where the magnetic lines of force are theweakest.
 20. An apparatus as defined in claim 1, wherein either theupper or the lower half of the magnetic member is removable so as tofacilitate replacement of the induction coil.
 21. An electromagneticedge containment device for a belt casting system for casting moltenmetal, the containment device comprising: a magnetic member having afirst pole, a first pole face, a second pole, and a second pole face;and a coil that generates magnetic lines of force in the magnetic memberwhen current is supplied to the coil, the magnetic lines of forcepassing from the first pole face through an edge of the belt castingsystem to the second pole face.
 22. An apparatus in accordance withclaim 21, further comprising the belt casting system, the belt castingsystem having two belts that mold the molten metal.
 23. An apparatus inaccordance with claim 22, wherein the magnetic lines of force containthe molten metal in an edge region between the two belts.
 24. Anapparatus in accordance with claim 22, wherein the two belts have acurved region and a linear region.
 25. An apparatus in accordance withclaim 24, wherein the magnetic lines of force contain the molten metalin a region between the curved region of the two belts.
 26. An apparatusin accordance with claim 22, wherein each belt has an edge that passeswithin a region between the first pole face and the second pole face.27. An apparatus in accordance with claim 24, further comprising apulley defining the curved region and a shield positioned between themagnetic member and the pulley to shield the pulley from the magneticlines of force.
 28. An apparatus in accordance with claim 26, whereinthe belts have a curved region in a gap between the first pole face andthe second pole face.
 29. An apparatus in accordance with claim 28,wherein the first pole face and the second pole face become fartherapart along the curved region.
 30. An apparatus in accordance with claim29, wherein a mechanical edge dam is located in a region along the beltswhere a gap between the first pole face and the second pole face is at amaximum.
 31. An apparatus in accordance with claim 21, furthercomprising an outer shield surrounding the magnetic member so as tocontain the magnetic lines of force within the magnetic member.
 32. Anapparatus in accordance with claim 21, further comprising an innershield positioned within the magnetic member so as to contain themagnetic lines of force within the magnetic member.
 33. An apparatus inaccordance with claim 21, wherein the magnetic member includes a coolingpassage for cooling the magnetic member.
 34. An apparatus in accordancewith claim 21, wherein the belts have a thickness which increasestowards an outer edge thereof.
 35. An apparatus in accordance with claim23, wherein the first pole face is not parallel to the second pole face.36. An apparatus in accordance with claim 23, wherein the first poleface is parallel to the second pole face.
 37. An apparatus in accordancewith claim 23, wherein the first pole face and the second pole face havea first opposed surface parallel to each other and a second opposedsurface not parallel to each other.
 38. An apparatus in accordance withclaim 23, wherein a distance between the first pole face and the secondpole face is greater at an outside edge of each pole face than at aninside edge of each pole face.
 39. An apparatus in accordance with claim23, wherein a distance between the first pole face and the second poleface is greater at the inside edge of each pole face than at an outsideedge of each pole face.
 40. An apparatus in accordance with claim 21,wherein the magnetic member is formed of a ferromagnetic material from astack of bonded elements.
 41. An apparatus in accordance with claim 21,wherein the magnetic member is formed of a ferromagnetic material from aplurality of sections that are mechanically held together.
 42. Anapparatus in accordance with claim 21, wherein the magnetic member isformed from a solid core of ferromagnetic material.
 43. An apparatus inaccordance with claim 21, wherein the first pole and/or the second poleis removably attached to the magnetic member so as to facilitatereplacement of the coil.
 44. A method of containing molten metal betweentwo belts in a strip casting system, said method comprising the stepsof: delivering molten metal to a molding zone at an upstream end of thebelts; solidifying the molten metal into a strip between the belts andconveying the strip between the belts in a downstream direction;containing molten metal at later edges of the belts in the molding zoneby providing electrical current to a coil around a magnetic member togenerate magnetic lines of force which contain the molten metal; windinga coil around a magnetic member having an upper pole face and a lowerpole face; positioning the magnetic member so that the upper pole faceand a lower pole face overlay a lateral edge of each belt; and,providing electrical current to the coil to generate magnetic lines offorce.
 45. An apparatus in accordance with claim 1 wherein the polefaces are not smooth.
 46. An apparatus in accordance with claim 21wherein the pole faces are not smooth.